Desmoplastic small round cell tumor (DSRCT) is a rare but extremely aggressive cancer arising in young adolescents in the abdominal area. In all cases of DSRCT examined to date, a chromosomal translocation involving the Ewings Sarcoma gene (EWS) and the Wilms tumor suppressor gene, WT1, results in the fusion of the two genes, generating a novel transcription factor. In Ewing's sarcoma, which is a different type of pediatric tumor, EWS gene is fused to the Fli-1 gene, an ETS-family of transcription factor. Our interest is focused on understanding the molecular functions of EWS/WT1 and EWS/Fli1 gene products and how they contribute to tumorigenesis in their respective cancers. Towards this goal, we are currently developing mouse models of DSRCT and Ewing's sarcoma to better understand the etiology and the development of these tumors in the context of living organism. Aim 1. We will generate mouse models of these cancers with similar chromosomal tranlocations that are found in DSRCT and Ewing's sarcoma by using gene targeting approach. Successfully targeted mouse ES cells will then be injected to generate mice harboring these chromosomal translocations. Aim 2. We will examine the mice for the formation of spontaneous tumors and also to introduce secondary mutations by intercross with other cancer-prone animal models in hopes of accelerating tumorigenesis. Aim3. We will generate cell lines expressing the EWS/WT1 and EWS/Fli-1 translocations, either from the animals or from the tumors that are formed, and perform expression profiling analysis as well as proteomics (mass spectrometry) to identify tumorigenic pathways and interacting proteins that drive transformation. Our mouse models will help elucidate molecular mechanisms of these pediatric cancers and the knowledge gained will also shed light on the other adult tumors with similar characteristics. Our models will also be invaluable for the development of new therapeutics against DSRCT and Ewing'sarcoma.